Bevilacqua M et al. (2006) Dissimilar PTH, gastrin, and calcitonin responses to oral calcium and peptones in hypocalciuric hypercalcemia, primary hyperparathyroidism, and normal subjects: a useful tool for differential diagnosis. J Bone Min Res 21: 406–412

It is important to distinguish between primary hyperparathyroidism (PH) and hypocalciuric hypercalcemia (HH), as failure to diagnose the latter might result in unnecessary surgery. Differential diagnosis can be difficult without genetic testing, which is costly and not routinely available in clinical practice. An Italian team has identified a new way to distinguish between the two disorders, by demonstrating that PH and HH patients respond differently to PEPTONES.

Bevilacqua et al. assessed the effect of oral calcium and peptones (they used a mixture of L-amino acids that are known to activate calcium-sensing receptors) on levels of gastrin, parathyroid hormone, and calcitonin in 15 patients with PH, 10 patients with HH, and 30 healthy controls. They found that the mean gastrin and calcitonin responses to oral calcium of both the PH and HH patients were markedly lower than those of the controls. The same pattern was observed for responses to peptones; however, a significantly higher parathyroid hormone response was seen in PH patients than in either HH patients or controls.

This finding points towards there being a simple, clinically useful test that can distinguish between PH and HH. In addition, the authors suggest that the observed lack of normal responses to oral calcium and peptones might reflect the generally decreased sensitivity of the calcium-sensing receptor in patients with PH and HH.